In LTE-A (Long Term Evolution Advanced), there has been examined the introduction of a radio relay station (RN: Relay Node) which includes a function of wirelessly relaying for the purpose of expanding the coverage of a radio base station (eNB: enhanced Node B), eliminating a dead zone or the like, and thus the development of specifications of the radio relay station is under way. Further, among various types of radio relay stations, it has been decided to employ a radio relay station (Type1 RN) that relays layer 3 information (for example, see NPL 1).
The Type1 RN includes a function of transmitting/receiving signals to/from a mobile station (UE: User Equipment) as with the eNB. Further, the Type1 RN includes a function of transmitting/receiving signals between the Type1RN itself and its serving radio base station (DeNB: Donor eNB). Note that in the subsequent description, the term “eNB” indicates the DeNB. Further, a radio interface between the RN and the eNB is referred to as “Backhaul Link”, and a signal transmitted through the Backhaul Link is referred to as “backhaul signal”. On the other hand, a radio interface between the RN and the UE is referred to as “Access Link”, and a signal transmitted through the Access Link is referred to as “access-link signal”.
The frequency band of a downlink access-link signal from the Type1 RN to the UE is equal to that of a downlink backhaul signal from the eNB to the Type1 RN. Further, the frequency band of an uplink access-link signal from the UE to the Type1 RN is equal to that of an uplink backhaul signal from the Type1 RN to the eNB.
Accordingly, in a mobile communication system to which the Type1 RN is applied, signals in the same frequency are basically handled in a time-division manner. The eNB performs control on scheduling in the time-division manner.
Note that as variations of the Type1 RN, there will be defined a Type1a RN which uses mutually different frequency bands for the backhaul signal and the access-link signal, and a Type1b RN which uses the same frequency band for the backhaul signal and the access-link signal but ensures spatial isolation (in other words, need not handle signals in the time-division manner). Meanwhile, the present invention can be applied to each and every one of the Type1 RN, the Type1a RN, and the Type1b RN. Therefore, in the subsequent description, the Type1 RN, the Type1a RN and the Type1b RN are collectively referred to as “RN” without distinguishing one from another. Further, in some cases, the radio relay station (RN) is abbreviated as “relay station”, and the radio base station (eNB) is abbreviated as “base station”.
Further, in the RAN meeting of 3GPP (RAN#60, February 2010), it was agreed that only a Fixed RN would be considered as the RN in the beginning of practical applications of the LTE-A (Release 10). The Fixed RN means, as its name suggests, a radio relay station which does not move in principle after the placement thereof.
On the other hand, in the future, it will be imperative to introduce a Mobile RN which can accommodate moving UEs by placing the Mobile RN within a bus, a train, or the like. With the introduction of the Mobile RN, it is predicted that the Fixed RN and the Mobile RN may be inevitably mixed within a cell formed by an identical eNB (in other words, the both RNs may be connected to the same eNB).